1. Field of the Invention
The present invention relates to a system for determining the fully-closed state of a subsidiary throttle valve disposed in series with a main throttle valve mounted in an intake passage in an engine.
2. Description of the Prior Art
For example, in an engine of a vehicle including a traction control device, a main throttle valve connected to an accelerator pedal and opened and closed by the accelerator pedal, and a subsidiary throttle valve connected to an actuator and opened and closed by the actuator are mounted in series. And when an excessive slipping of a driven wheel occurs, the subsidiary throttle valve is controlled to be closed, thereby reducing the output from the engine to suppress the excessive slipping.
To accurately control the opening degree of the subsidiary throttle valve, it is necessary to correctly detect the opening degree of the subsidiary throttle valve. For this purpose, a system for determining the fully-opened state of the subsidiary throttle valve has been proposed (see Japanese Patent application Laid-open No.107926/81). This prior art system is designed such that when the actuator for opening and closing the subsidiary throttle valve is in a non-energized state and the subsidiary throttle valve is in a fully opened state, the fully opened state is determined by detecting it by a sensor and storing it.
The subsidiary throttle valve is normally in an opened state and is closed when the traction control device is operated. However, the important opening degree of the subsidiary throttle valve for suppressing the excessive slipping of the driven wheel, is near a substantially fully-closed state. For this reason, the system for determining the fully-closed state of the subsidiary throttle valve as in the prior art is accompanied by a problem that it is impossible to carry out an effective determining.
In order to avoid such disadvantage, it may be conceived that the fully-closed state of the subsidiary throttle valve should be determined. However, if the subsidiary throttle valve is brought into a fully-closed state, an influence is exerted to the operational state of the engine and hence, it is necessary to determine the fully-closed state while selecting a particular operational state (e.g., an idling state) in which such influence is minimized. However, even if all of a plurality of conditions in which the engine is in the above-described particular operational state are satisfied and the subsidiary throttle valve is closed to conduct the determining, the closing of the subsidiary throttle valve must be discontinued once whenever any of these conditions not satisfied. And when all of the conditions are satisfied again, the closing of the subsidiary throttle valve is carried out again. Consequently, the actuator for opening and closing the subsidiary throttle valve is intermittently driven, resulting in disadvantages such as generation of a noise, an increase in consumed electric power and the like.